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State-Specific Rates of Primary and Secondary Syphilis Among Men Who Have Sex with Men — United States, 2015

Summary

What is already known about this topic?

Syphilis rates in the United States have been steadily increasing since 2001, and gay, bisexual, and other men who have sex with men (collectively referred to as MSM) represent a disproportionate number of cases. In the absence of reliable, state-specific denominators it has been difficult to estimate state-specific rates and rate ratios to accurately measure the geographic variation and disparity.

What is added by this report?

State-specific rate ratios comparing the rate of syphilis among MSM with the rate among men reporting sex with women only ranged from 39.2 (Minnesota) to 342.1 (Hawaii); overall, MSM had a rate of primary and secondary syphilis 106.0 times the rate among men who reported sex with women only.

What are the implications for public health practice?

These state-specific rates further highlight the disproportionate impact of syphilis among MSM. Providers should screen sexually active MSM for syphilis at least annually and provide timely treatment according to national sexually transmitted diseases treatment guidelines.

In 2015, the rate of reported primary and secondary syphilis in the United States was 7.5 cases per 100,000 population, nearly four times the previous lowest documented rate of 2.1 in 2000 (1). In 2015, 81.7% of male primary and secondary syphilis cases with information on the sex of the sex partner were among gay, bisexual, and other men who have sex with men (collectively referred to as MSM) (1). These data suggest a disproportionate incidence of disease among MSM. However, attempts to quantify this disparity have been hindered by limited data on the size of the MSM population at the state level. To produce the first estimates of state-specific rates of primary and secondary syphilis among MSM, CDC used MSM population estimates based on a new methodology (2) and primary and secondary syphilis case counts reported in 2015 to the National Notifiable Diseases Surveillance System. Among 44 states reporting information on the sex of sex partners for ≥70% of male cases, the overall rate of primary and secondary syphilis among all men (aged ≥18 years) in the United States in 2015 was 17.5 per 100,000, compared with 309.0 among MSM and 2.9 among men who reported sex with women only. The overall rate of primary and secondary syphilis among MSM was 106.0 times the rate among men who have sex with women only and 167.5 times the rate among women.* These data highlight the disproportionate impact of syphilis among MSM and underscore the need for innovative and targeted syphilis prevention measures at the state and local level, especially among MSM. It is important that health care providers recognize the signs and symptoms of syphilis, screen sexually active MSM for syphilis at least annually, and provide timely treatment according to national sexually transmitted diseases treatment guidelines (3).

Case reports of primary and secondary syphilis cases for MSM, men who have sex with women only, and women were obtained from national data reported regularly by all states for 2015. These data include limited demographic and clinical information, including the sex of sex partners. Population estimates of the number of MSM by state were obtained using new methodology that makes use of census and population-based survey data (2). To estimate the MSM population size, the estimated percentage of MSM among men was adjusted (4) according to each U.S. county’s percentage of households with a male head and a male partner, obtained from American Community Survey summary data and urban-rural classification (large central metropolitan, large fringe metropolitan, medium or small metropolitan, or nonmetropolitan or rural) from the National Center for Health Statistics (4). The county’s percentage of MSM was adjusted according to the ratio of its percentage of male same-sex households to the overall percentage among all counties at the same urban-rural classification, which was then multiplied by the number of men in the county to achieve the estimated MSM population size. This final number was then scaled to equal 3.9% of the adult male population, based on a prior national MSM estimate (5).

To optimize stability of the estimates, the analysis was limited to the 44 states that included sex of sex partner in ≥70% of male primary and secondary syphilis case reports for 2015. The 70% threshold represented the best balance between including male cases of primary and secondary syphilis while gathering the most complete epidemiologic data for those cases. State-specific rates of primary and secondary syphilis among MSM were compared with rates of primary and secondary syphilis among men who have sex with women only and also among women (cases in men with unknown sex of sex partner were excluded from this analysis). Rate ratios were calculated as 1) the rate of primary and secondary syphilis among MSM divided by the rate among men who have sex with women only and 2) the rate among MSM divided by the rate among women.†

Primary and secondary syphilis cases in the 44 states included in the analysis accounted for 83.4% of all 23,872 reported primary and secondary syphilis cases in the United States in 2015. Among the reported primary and secondary syphilis cases among men and women in these 44 states in 2015, 12,118 (60.8%) were among MSM, including 10,942 (54.9%) among men who had sex with men only and 1,176 (5.9%) cases among men who had sex with both men and women.

Among the 44 states, the overall rates of primary and secondary syphilis in 2015 among all men, MSM, men who have sex with women only, and women were 17.5, 309.0, 2.9, and 1.8 cases per 100,000 population, respectively. State-specific rates among MSM ranged from 73.1 per 100,000 population (Alaska) to 748.3 (North Carolina) (Table 1). The overall U.S. rate of primary and secondary syphilis among MSM was 106.0 times the rate among men who have sex with women only, with state-specific rate ratios ranging from 39.2 (Minnesota) to 342.1 (Hawaii). The overall rate of primary and secondary syphilis among MSM was 167.5 times the rate among women, with state-specific rate ratios ranging from 63.7 (Louisiana) to 2,140.3 (Hawaii).

Rates of primary and secondary syphilis among MSM varied by U.S. Census region and by state, with the highest rates in the South and West. Four of the five states with the highest primary and secondary syphilis rates among MSM were southern states (Louisiana, Mississippi, North Carolina, and South Carolina) (Table 2). Among states with the 10 highest rates of primary and secondary syphilis in the United States in 2015 (1), five states (Arizona, Louisiana, Mississippi, Nevada, and North Carolina) also ranked among the top 10 states with the highest rates of primary and secondary syphilis among MSM (Table 2).

Discussion

These are the first state-specific rates of primary and secondary syphilis reported for MSM in the United States. The lowest state-specific MSM primary and secondary syphilis rate (73.1 in Alaska) exceeded the highest overall U.S. primary and secondary syphilis rate (70.9), which was observed in 1946. In every state, the incidence of reported syphilis among MSM was higher than the incidence among men who have sex with women only, with rate ratios ranging from 39.2 to 342.1. These data support CDC’s earlier findings using national population size estimates, which highlighted national disparities in syphilis incidence. In the earlier findings, the rate of syphilis incidence among MSM was estimated to be 154 per 100,000 population, compared with 2.2 per 100,000 among other men, resulting in a rate ratio of 71 (5), in comparison to the estimate of 106.0 in the current analysis. However, the previous findings were limited in their applicability to state or local areas because the percentage of adult males who are MSM varies widely among states.

Although state-specific incidence rates varied, even in low incidence states (e.g., North Dakota), syphilis rates among MSM were higher than those among men who have sex with women only. The geographic variation highlights the importance of these data for state and local health departments, which can use these data to better understand their local syphilis epidemiology and target resources and interventions to address disparities between MSM and other population groups. The comparison of state-specific rates also highlights the high disease incidence in the South. Four of the five states with the highest primary and secondary syphilis incidence rates among MSM in 2015 were southern states. The estimates of state-specific rates among men who have sex with women only, although lower than those among MSM, also have implications for the rates of syphilis among women. Trends in congenital syphilis tend to follow trends in the incidence of primary and secondary syphilis among women of reproductive age, which has been increasing recently (6). Congenital syphilis can result in serious health consequences in infants (6). Although CDC is limited by its data usage agreement with the Council of State and Territorial Epidemiologists to conduct data analysis at the state level (7), further analyses at the county level by state and local health jurisdictions could be helpful to inform public health action by elucidating geographic disparities in greater detail.

The findings in this report are subject to at least four limitations. First, analyses were restricted to states where the sex of sex partners (male, female, or both) was reported for ≥70% of male cases of primary and secondary syphilis cases during 2015. Although 83.4% of all reported primary and secondary syphilis reported in the United States during 2015 were included, these jurisdictions might not be representative of all persons who receive a diagnosis of primary and secondary syphilis. Second, the denominators used in calculating the rates of primary and secondary syphilis were estimates of the number of MSM in each state, based on the reporting of same-sex households in the American Community Survey; underreporting of same-sex households could result in an underestimation of the MSM population and an overestimation of primary and secondary syphilis rates. Third, cases of syphilis in men for whom the sex of sex partners was unknown were excluded in calculations for both MSM and men who have sex with women only. If MSM are more likely to underreport the sex of their sex partner, this might result in an underestimation of the rate of syphilis among MSM and consequent rate ratio when comparing syphilis rates among MSM and men who have sex with women only. Improving the quality of case report data regarding sex of sex partner information could increase the awareness of public health officials regarding the characteristics of syphilis within their communities. Finally, primary and secondary syphilis case report data likely underestimate the actual number of incident syphilis infections in the United States because not all infections are diagnosed and reported (8).

Despite these limitations, these findings are consistent with previous reports that showed pronounced disparities in primary and secondary syphilis rates between MSM and men who have sex with women only (5), and the use of state-specific MSM population sizes and primary and secondary syphilis case counts permits comparison of primary and secondary syphilis rates by state. Rates among MSM compared with men who have sex with women only were higher in every state, but state-specific data suggested that certain states might have a greater need for syphilis prevention. Because MSM represent the majority of all primary and secondary syphilis cases, the success of syphilis prevention programs is contingent upon addressing the high rates of syphilis among MSM. It is important that both private and public health care providers 1) recognize the signs and symptoms of syphilis, 2) conduct a comprehensive sexual history, 3) screen all sexually active MSM for syphilis at least annually, and 4) provide timely treatment according to national sexually transmitted diseases treatment guidelines (3). Part of this sexual history includes eliciting information on sexual practices and the sex of patients’ sex partners.§

* In this report “women” is used to describe both females aged ≥18 years (used for calculating rates for women) and females of unknown ages (used for calculating rates for men who had sex with women only).

References

Grey JA, Bernstein KT, Sullivan PS, et al. Estimating the population sizes of men who have sex with men in US states and counties using data from the American Community Survey. JMIR Public Health Surveill 2016;2:e14. CrossRefPubMed

Purcell DW, Johnson CH, Lansky A, et al. Estimating the population size of men who have sex with men in the United States to obtain HIV and syphilis rates. Open AIDS J 2012;6(Suppl 1):98–107. CrossRefPubMed

TABLE 1. Rates and rate ratios for primary and secondary syphilis among men who have sex with men (MSM), among men who have sex with women only, and among women, by state and overall — United States, 2015*

State†

MSM

Rate of primary and secondary syphilis per 100,000 population

Rate ratio§

Estimated no. in population

% of all men

MSM

Men who have sex with women only

Women

MSM compared with men who have sex with women only

MSM compared with women

Overall

3,921,515

3.8

309.0

2.9

1.8

106.0

167.5

Alabama

41,822

2.3

320.4

2.4

1.9

131.5

169.4

Alaska

5,469

1.9

73.1

1.1

0.4

67.8

189.5

Arizona

112,102

4.5

385.4

3.3

1.7

116.1

222.0

Arkansas

19,101

1.7

314.1

3.4

2.2

92.9

140.6

California

796,926

5.5

332.2

3.9

3.1

85.8

108.0

Colorado

74,742

3.6

248.9

1.2

0.2

205.5

1,023.7

Connecticut

43,542

3.2

112.5

0.7

1.0

162.7

117.6

Florida

351,797

4.6

370.1

4.5

2.4

82.7

152.3

Hawaii

15,707

2.8

388.4

1.1

0.2

342.1

2,140.3

Idaho

9,979

1.7

320.7

2.4

1.3

131.0

242.7

Illinois

199,075

4.1

311.9

2.5

1.5

124.6

203.8

Indiana

72,413

3.0

290.0

1.5

1.1

193.3

266.6

Iowa

20,924

1.8

219.8

1.0

0.4

226.7

531.7

Kansas

21,906

2.0

228.2

1.3

1.4

169.6

168.1

Kentucky

47,576

2.9

159.7

1.9

1.3

84.5

126.8

Louisiana

43,204

2.5

601.8

8.4

9.5

71.9

63.7

Maine

14,375

2.8

118.3

0.4

1.1

295.3

108.9

Maryland

83,668

3.8

325.1

4.5

2.4

72.0

137.9

Massachusetts

110,254

4.3

278.4

1.1

0.9

247.3

324.2

Michigan

116,354

3.1

233.8

1.4

0.8

163.8

280.2

Minnesota

82,510

4.0

147.9

3.8

1.7

39.2

87.0

Mississippi

20,184

1.9

658.9

4.1

2.6

161.0

251.3

Missouri

72,875

3.2

204.5

3.8

2.2

53.9

93.0

Montana

6,800

1.7

132.4

0.5

0.0

254.1

—¶

Nevada

51,990

4.8

398.2

4.9

1.8

81.3

216.6

New Hampshire

13,868

2.7

187.5

1.2

0.6

155.3

337.8

New Jersey

136,271

4.1

152.6

1.3

0.7

117.2

219.3

New Mexico

18,675

2.4

428.4

2.5

1.4

169.2

314.0

North Carolina

105,707

2.9

748.3

5.3

2.7

140.0

278.2

North Dakota

4,840

1.7

165.3

1.1

0.0

150.4

—

Ohio

146,033

3.4

214.3

2.9

1.4

73.3

157.5

Oklahoma

37,006

2.6

418.9

2.3

1.4

185.4

297.6

Oregon

60,932

4.0

313.5

2.8

2.2

111.9

142.1

Pennsylvania

162,848

3.3

256.1

1.6

0.8

159.3

310.5

Rhode Island

24,745

6.1

226.3

2.7

0.9

84.6

248.9

South Carolina

35,388

2.0

536.9

2.9

1.7

187.8

307.9

South Dakota

4,937

1.5

405.1

2.6

2.2

156.2

186.2

Tennessee

73,460

3.0

325.3

2.8

0.9

115.4

371.3

Texas

378,310

3.9

289.4

3.2

2.2

90.1

133.9

Utah

33,898

3.3

132.8

0.5

0.2

251.1

679.2

Vermont

7,142

2.9

126.0

0.0

0.0

—

—

Virginia

115,515

3.7

210.4

1.5

0.5

138.3

436.0

Washington

113,504

4.2

306.6

1.9

1.1

160.6

290.6

West Virginia

13,141

1.8

197.9

2.3

1.2

87.2

165.0

* Data based on 2015 cases reported to CDC by June 8, 2016.† To optimize stability of the estimates, the analysis was limited to the 44 states that included sex of sex partner in ≥70% of male primary and secondary syphilis case reports for 2015.§ Rate ratios were calculated as 1) the rate of primary and secondary syphilis among MSM divided by the rate among men who have sex with women only and 2) the rate among MSM divided by the rate among women. In this report “women” is used to describe both females aged ≥18 years (used for calculating rates for women), and females of unknown ages (used for calculating rates for men who had sex with women only). Rate ratios were rounded to tenths.¶ Montana, North Dakota, and Vermont had no cases of primary and secondary syphilis reported among women for 2015, resulting in an undefined rate ratio comparing MSM with women. Vermont had no cases of primary and secondary syphilis reported among men who had sex with women only in 2015, resulting in an undefined rate ratio comparing MSM with men who have sex with women only..

TABLE 2. States ranked from highest to lowest, by rates of primary and secondary syphilis cases overall and among men who have sex with men (MSM) and men who have sex with women only, and by rate ratios comparing the rates for MSM with the rates for men who have sex with women only and the rates for women — United States, 2015*

Rank†

Rate of primary and secondary syphilis per 100,000 population

Rate ratio§

Overall primary and secondary syphilis

Primary and secondary syphilis among MSM

Primary and secondary syphilis among men who have sex with women only

MSM compared with men who have sex with women only

MSM compared with women

1

Louisiana

North Carolina

Louisiana

Hawaii

Hawaii

2

California

Mississippi

North Carolina

Maine

Colorado

3

North Carolina

Louisiana

Nevada

Montana

Utah

4

Nevada

South Carolina

Maryland

Utah

Iowa

5

Florida

New Mexico

Florida

Massachusetts

Virginia

6

Arizona

Oklahoma

Mississippi

Iowa

Tennessee

7

Oregon

South Dakota

California

Colorado

New Hampshire

8

Maryland

Nevada

Missouri

Indiana

Massachusetts

9

Illinois

Hawaii

Minnesota

South Carolina

New Mexico

10

Mississippi

Arizona

Arkansas

Oklahoma

Pennsylvania

11

Rhode Island

Florida

Arizona

Kansas

South Carolina

12

Hawaii

California

Texas

New Mexico

Oklahoma

13

Washington

Tennessee

Ohio

Michigan

Washington

14

Texas

Maryland

South Carolina

Connecticut

Michigan

15

Massachusetts

Idaho

Tennessee

Mississippi

North Carolina

16

South Carolina

Alabama

Oregon

Washington

Indiana

17

Alabama

Arkansas

Rhode Island

Pennsylvania

Mississippi

18

New Mexico

Oregon

South Dakota

South Dakota

Rhode Island

19

Oklahoma

Illinois

New Mexico

New Hampshire

Idaho

20

Tennessee

Washington

Illinois

North Dakota

Arizona

21

Pennsylvania

Indiana

Idaho

North Carolina

New Jersey

22

Missouri

Texas

Alabama

Virginia

Nevada

23

Ohio

Massachusetts

West Virginia

Alabama

Illinois

24

Colorado

Pennsylvania

Oklahoma

Idaho

Alaska

25

South Dakota

Colorado

Washington

Illinois

South Dakota

26

Arkansas

Michigan

Kentucky

New Jersey

Alabama

27

Minnesota

Kansas

Pennsylvania

Arizona

Kansas

28

Indiana

Rhode Island

Virginia

Tennessee

West Virginia

29

New Jersey

Iowa

Indiana

Oregon

Ohio

30

Michigan

Ohio

Michigan

Arkansas

Florida

31

Virginia

Virginia

Kansas

Texas

Oregon

32

Idaho

Missouri

New Jersey

West Virginia

Arkansas

33

Kentucky

West Virginia

Colorado

California

Maryland

34

New Hampshire

New Hampshire

New Hampshire

Rhode Island

Texas

35

Kansas

North Dakota

Hawaii

Kentucky

Kentucky

36

West Virginia

Kentucky

Massachusetts

Florida

Connecticut

37

Connecticut

New Jersey

North Dakota

Nevada

Maine

38

Iowa

Minnesota

Alaska

Ohio

California

39

Utah

Utah

Iowa

Maryland

Missouri

40

Maine

Montana

Connecticut

Louisiana

Minnesota

41

North Dakota

Vermont

Utah

Alaska

Louisiana

42

Vermont

Maine

Montana

Missouri

—¶

43

Montana

Connecticut

Maine

Minnesota

—

44

Alaska

Alaska

Vermont

—

—

* Data based on 2015 cases reported to CDC by June 8, 2016.† To optimize stability of the estimates, the analysis was limited to the 44 states that included the sex of sex partners in ≥70% of male primary and secondary syphilis case reports for 2015.§ Rate ratios were calculated as 1) the rate of primary and secondary syphilis among MSM divided by the rate among men who have sex with women only and 2) the rate among MSM divided by the rate among women. In this report “women” is used to describe both females aged ≥18 years (used for calculating rates for women), and females of unknown ages (used for calculating rates for men who had sex with women only).¶ Montana, North Dakota, and Vermont had no cases of primary and secondary syphilis reported among women for 2015, resulting in an undefined rate ratio comparing MSM with women. Vermont had no cases of primary and secondary syphilis reported among men who had sex with women only in 2015, resulting in an undefined rate ratio comparing MSM with men who have sex with women only..

Suggested citation for this article: de Voux A, Kidd S, Grey JA, et al. State-Specific Rates of Primary and Secondary Syphilis Among Men Who Have Sex with Men — United States, 2015. MMWR Morb Mortal Wkly Rep 2017;66:349–354. DOI: http://dx.doi.org/10.15585/mmwr.mm6613a1.

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